Amplifier coupling network



Jan.. 17, 1950 ..1. HAANTJES AMPLIFIER coUPLING NETWORK Filed Feb. ll,1947 /NvENTaR .JOHAN HAAN'N Es ev/ @W GENT Patented `ian. 17, 1950AMPLIFIER COUPLING NETWORK Johan Haantjes, Eindhoven, Netherlands, as-

signor to Hartford National Bank and Trust Company, Hartford, Conn., astrustee Application February 11, 1947, Serial No. 727,852 In theNetherlands March 11, 1944 Section 1, Public Law 690, August 8, 1946Patent expires March 11, 1964 2 Claims.

In View of suppressing or at least reducing the linear distortion inresistance-condenser coupled amplifiers, which is manifest by anamplification characteristic dropping towards the low frequencies, it isknown to connect in series with the resistance Ra in the anode circuitof an amplifying tube l (see Fig. 1) a condenser C which is shunted by aresistance R in regard to the direct anode current. When choosing C insuch a manner as to satisfy the relation:

where C designates the coupling condenser and Rg represents the leakageresistance in the grid circuit of the next amplifying tube 2, theamplification i. e. the ratio of the voltages Ez/E is independent of thefrequency even in regard to very low frequencies.

This solution, however, is only serviceable if the internal resistanceof the amplifying tube I is high with respect to the total impedance ofthe anode circuit. In the case of this condition not being satisfied, sothat the internal resistance is low relatively to the total impedance inthe anode circuit, the voltage across the series connection of Ra and Cwill be free from linear distortion and, due to the frequency-dependentvoltage distribution over C and Rg, a frequency-dependent voltage is setup across Rg. Hence, the amplification E'z/E is dependent with respectto the frequency, in other words linear distortion occurs.

The same problem is generally encountered in circuits for thetransmission of alternating voltages having different frequencies, whichappear between a pair of input terminals 3, 4 (vide Fig. 2) to a pair ofoutput terminals 5, 6, the two pairs of terminals being decoupled inregard to direct current by means of a condenser C, and a resistance Rbeing interposed between the output terminals. The condenser C bringsabout an output voltage which decreases with a decrease in frequency, sothat the voltage ratio Ez/E is dependent with respect to frequency inregard to low frequencies.

According to the invention, in order to obtain a practicallydistortion-free transmission, a resistance R is connected in series withthe condenser C and a condenser C is connected in se- 2 ries with theresistance R, whilst R and Ci are so chosen as to satisfy the relationFig. 3 represents the circuit arrangement according to the invention. Ananalysis of the voltages existing across the impedances at Ez and E' canbe determined by Kirchoff's law:

and,

0 a FR then i E; -R+R1 R E2-E1R Rl from which it appears that thevoltage ratio is independent of the frequency.

Fig. 4 depicts the use of the circuit according to the invention in aresistance-coupled amplifier. It is assumed that the internal resistanceof the first amplifying tube I is low with respect to the totalimpedance in the anode circuit which is constituted by theparallel-connection of the anode resistance Ra and the series-connectionof the coupling condenser C, the resistances R and R and the condenserC'. When this condition is satisfied the amplified voltage across Ra ispracpendent with respect to frequency in regard to v very lowfrequencies, it is true, butx if lthe resistance Rg is so chosen as tobe high, in regard to the said circuit elements relating in magnitudeaccording to the equation:

(If-R 2. An electric circuit arrangement comprising a first thermionicdischarge tube having a cathode, grid and anode, a second thermionicdischarge tube having a cathode, grid and anode, said second thermionicdischarge tube having further -a capacity between the grid and cathodehaving a 'value Cgk, and means to couple the .anode-cathode circuit ofsaid first thermionic V dischargetube to the grid-cathode circuit ofsaid the lowest frequency to be amplified, with respect to the reactanceof condenser C, this influence will practically not disturb.

In the ampliiying circuit shown in -Fig..4 thegrid-cathode capacity Cgkavailable betweenV the grid and the cathode of the amplifying, tube 2.

involves a dropping amplification characteristic at high frequencies.This disturbance can be made up for by connecting a condenser Cz iinparallel with the series connection of C and R or, whichinpractice'comes to the-same, in parallel with R and by giving it such asize that 02 I t Cgk Rl Of course, the same expedient may also be usedin the circuit shown in Fig. 3, if a certain capacity be availablebetween the output terminals 5, 6.

What I claim is: L. An electric circuit arrangement comprising a pair ofinput terminals, a pair of output terminals, a first capacitive elementhaving a value- C and a first-resistive element 'having a value Riconnected in series 'between'one of the said input and one of saidoutput terminals, a second capacitive element having a value C and asecond resistive element having a value R connected in series betweenthe said output terminals, and

second thermionic discharge tube, said latter mmeansfcornprising a firstcapacitive element havv inga value C and a first resistive elementhaving a value R connected in series between the anode- =cathode circuitof .said first thermionic discharge -tube and the grid-cathode circuitof said second thermionic discharge tube, a, second capacitive ;elementhaving a value C and a second resistive element having a value Rconnected in series in the grid-cathode circuit of said secondthermionic discharge tube, a third capacitive element having a valueCzt-in Vparallel with. said first resistive element, `andthe saidcircuitelements relating'inma-gnitude according to the equation:

9:11): 22 Ci Rl Cgk JOHANHAANTJ ES.

REFERENCES CITED The following references yare of record in the file ofthis patent:

UNITED STATES PATENTS Number. Name Date 2,045,316 Stocker June 23, 1936'2,120,323A white June 14, 1938i 2,212,205 Hepp Aug. 20,,1940 A2,243,121Preisman May 27, 1941 2,275,023 White Mar. 3, 1942v

